Temporal change of radiocarbon in the water column of the western North Pacific

Aramaki, Takafumi*; Togawa, Orihiko ; Watanabe, Shuichi*; Tsunogai, Shizuo*; Taira, Keisuke*

Radiocarbon data (C) were obtained in a wide range of surface and along the 165 degrees East in the western North Pacific between 1991 and 1993. The variability of C in surface water at north-south direction was larger than that at east-west direction, and C markedly decreased northward in the north of 40 degrees North. Comparing C data along 165 degrees East with the 1973 GEOSECS, it became clear that the bomb-produced C was transported from the surface to the intermediate layer in the sub-tropical region during the last 20 years, and not found in deep water in 1993. The distribution of the bomb-produced C and age of the deep water suggest that the sub-tropical bomb-C increase is caused from considerably storing in the intermediate layer originated in the sub-arctic region taken by vertical mixing and transported the North Pacific Intermediate Water flowing southward.